Penetration and cratering experiments of graphite by 0.5-mm diameter steel spheres at various impact velocities

https://doi.org/10.1016/j.ijimpeng.2014.03.004Get rights and content

Highlights

  • We present impact experiments of steel spheres onto graphite at various velocities.

  • Tomographies provided crater dimensions and projectile depths of penetration.

  • Crater dimensions are compared to previous works with similar materials.

  • We notice four regimes of penetration behavior.

  • A discussion of the physical mechanisms at play is proposed.

Abstract

Cratering experiments have been conducted with 0.5-mm diameter AISI 52100 steel spherical projectiles and 30-mm diameter, 15-mm long graphite targets. The latter were made of a commercial grade of polycrystalline and porous graphite named EDM3 whose behavior is known as macroscopically isotropic. A two-stage light-gas gun launched the steel projectiles at velocities between 1.1 and 4.5 km s−1. In most cases, post-mortem tomographies revealed that the projectile was trapped, fragmented or not, inside the target. It showed that the apparent crater size and depth increase with the impact velocity. This is also the case of the crater volume which appears to follow a power law significantly different from those constructed in previous works for similar impact conditions and materials. Meanwhile, the projectile depth of penetration starts to decrease at velocities beyond 2.2 km s−1. This is firstly because of its plastic deformation and then, beyond 3.2 km s−1, because of its fragmentation. In addition to these three regimes of penetration behavior already described by a few authors, we suggest a fourth regime in which the projectile melting plays a significant role at velocities above 4.1 km s−1. A discussion of these four regimes is provided and indicates that each phenomenon may account for the local evolution of the depth of penetration.

Introduction

One of the major concerns for spacecraft or high-power laser applications is the cratering process in brittle materials under high- and hyper-velocity impacts (HVI). Among them, carbon is of particular interest because it is a common elementary component in composite materials. Indeed, they are widely used in aerospace industry owing to their low density and high mechanical properties. In that specific case, meteoroids may impact satellites at several kilometers per second, possibly damaging or destroying some vital equipment [1], [2], such as tanks. Moreover, the ejection of secondary debris created by previous impacts can remain on orbital trajectories and hit other man-made space structures [3]. Similarly, the various instruments used in the Laser MégaJoule (LMJ) experiment chamber may be struck by a variety of shrapnel and debris originating from the target assembly after intense laser shots [4], [5].

The range of materials exposed to HVI is significant. Metals have been widely studied, both experimentally [6], [7], [8], [9] and through the use of numerical hydrocodes [10]. Brittle materials have also been included in previous studies, such as geophysical materials [11], silica glass [12], [13] or building materials [14], [15], [16]. For the latter, the depth of penetration (DOP) is particularly analyzed as a performance criterion. Concerning composites, studies have already been conducted [17], [18], but it appears there is a lack of knowledge about damaging and cratering processes of elementary components such as graphite matrix or fibers. Experimental results have been published giving crater dimensions in porous graphite for a variety of projectile materials and velocities [19], [20]. The present authors have attempted to compute numerical models into hydrocodes to reproduce experimental results [21]. However, a large set of experimental data was missing in order to fit the parameters of the models, especially that of the projectile such as elastic limit and strength which may be highly dependent of the strain rate [22].

In this paper, we present experiments leading to crater formation and penetration of a steel projectile into a commercial grade of polycrystalline graphite. In the following section, we describe the dynamic experiments on thick targets and display new results. Then, Section 3 will be devoted to the discussion of the data obtained by post-mortem tomographies on the recovered samples. Finally, in Section 4, we will try to get a better insight into the penetration processes.

Section snippets

Experimental

We recently conducted cratering experiments with 0.5-mm diameter AISI 52100 steel spherical projectiles and 30-mm diameter, 15-mm long graphite targets. This graphite is a commercial grade from the POCO company [23] and is macroscopically isotropic with a density of 1754 kg m−3. Its main mechanical characteristics have been published in Ref. [24] and are recalled in Table 1 along with those of hardened AISI 52100 steel. Indeed, projectiles stem from bearings involving a high Rockwell hardness

Crater depth and diameter

The crater diameters and depths normalized by the projectile diameter are plotted in Fig. 1. As expected, they strictly increase with the impact velocity, apparently following a power law. Previous studies about spherical projectiles impacting various ductile materials used a 2/3 power law which is linked to the hemispherical shape of the resulting craters [6], [7]. However, in the study of steel spheres impacting graphite brittle targets, Tanabe et al. [19] have noticed the same law with

Penetration without fragmentation (R1 and R2)

Here, we try to explain by two methods the successive increasing and decreasing of the projectile depth of penetration below 3.2 km s−1.

Take for example two shots with similar DOP yet different velocities, #68_13 (R1) and #72_13 (R2). It implies that the kinetic energy of the second is about 1 J greater than the first one. Consequently, the projectile of the second should be the deepest but that is not the case. Considering that #72_13 belongs to the regime where the projectile suffers plastic

Conclusion

We displayed new cratering and penetration experiments with 0.5-mm diameter steel spherical projectiles and thick cylindrical graphite targets at velocities between 1.1 and 4.5 km s−1. Post-mortem tomographies revealed that the projectiles were trapped into the target after the re-closing of the graphite. The characteristic dimensions of the craters such as volume, diameter and depth were measured and all of them increased with the impact velocity. But contrary to ductile materials, diameter

Acknowledgments

The authors express their gratitude to Stéphanie Tastet for performing the experiments and to Patrick Brelivet for the tomographies. They would also like to thank Claude Bianchi who accepted to revise the English of this paper.

References (29)

  • M. Forrestal et al.

    Penetration of grout and concrete targets with ogive-nose steel projectiles

    Int J Impact Eng

    (1996)
  • D. Numata et al.

    {HVI} tests on {CFRP} laminates at low temperature

    Int J Impact Eng

    (2008)
  • R. Tennyson et al.

    Hypervelocity impact damage to composites

    Compos Part A: Appl Sci Manuf

    (2000)
  • Y. Tanabe et al.

    Crater formation of carbon materials by impact of a high velocity sphere

    Carbon

    (1995)
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